1. Field of the Invention
The present invention relates to a heat exchanger and is effective for use for radiator which cools coolant water of a vehicle engine, an oil cooler of a vehicle transmission, and a heat exchanger in which a plurality of heat exchange media pass through separate paths.
2. Description of the Related Art
In the past, there has been known a core structure of a heat exchanger comprised of a plurality of tubes 2 through the inside of which an internal heat exchange medium passes, a plurality of fins 3 alternately stacked with the tubes and increasing the heat transfer of said heat exchange medium, core plates 5a to which the two ends of the tubes are connected, and side plates 7 arranged at the outsides in the stacking direction from the end fins 3a arranged at the outermost sides in the stacking direction of the fins and connected to the core plates 5a (see FIG. 1).
In this types of core structure of a heat exchanger, the tubes 2 and the corrugated fins 3 are alternately arranged between the two core plates 5a arranged facing each other across a predetermined distance. The two ends of the two core plates 5a are bridged by the side plates 7. Further, the two ends of the tubes 2 and the side plates 7 are inserted into the tube holes and the side plate holes provided at the core plates 5a and the insertion parts are brazed there (see FIG. 2).
However, in the aforementioned heat exchanger, when the heat exchange medium begins to pass through the tubes 2, the difference between the amount of heat expansion of the tubes 2 and the core plates 5a which directly receive the effect of the heat exchange medium and the amount of heat expansion of the side plates 7 which do not directly receive the effect of the heat exchange medium causes thermal stress accompanied with thermal strain in the tubes 2 and the side plates 7. Further, if thermal stress is repeatedly generated, there is the problem of fatigue breakage in the vicinities 7z of the joints (insertion part) of the tubes 2 and the side plates 7 in the core plates 5a. 
As a countermeasure, there is the art described in European Patent Publication No. 1001241.This bends parts of the side plates to enable the side plates to easily expand and contract in their longitudinal directions and absorb the amounts of heat expansion of the tubes and the side plates and thereby prevent in advance the parts where the tubes and the side plates are joined from fatigue breakage. Further, in the art described in Japanese Patent Publication (A) No. 2005-156068, the side plates are provided with zigzag slits to enable easily expansion and contraction perpendicular to the longitudinal direction. However, in these arts, the structures of the side plates are complicated, so production is not simple and the cost becomes high.
Further, when brazing the tubes and fins with the side plates, for example, wires or other jigs are used to arrange the side plates at the two outer sides of the tube and the fin assembly and these are brazed while simultaneously pressing these by a plurality of wires. (The set positions of the wires shown by the imaginary lines J in FIG. 2.) During this pressing operation, when using the side plates of the arts described in European Patent Publication No. 1001241 and Japanese Patent Publication (A) No. 2005-156068, since the side plates are low in rigidity, the tubes and fins cannot be uniformly pressed with the side plates and stable brazing is not possible.